A variety of problems can occur when you refinish wood with a varnish. Applying varnish on a moist or oily surface, applying too much varnish, applying different types of varnish on top of each other and applying varnish in overly warm environments are all common finishing problems that can lead to defects. Knowing what can go wrong with varnishing may help you avoid the problems and also improve your wood refinishing projects.
Crawling, Wrinkling and Tacky Varnish
According to Craftsman-Style.com, applying varnish to a moist or oily surface can lead to many different varnish defects. The varnish can "crawl," which occurs when the varnish does not adhere to the surface and appears like oil on water. Moisture may also cause the varnish to become runny, or to sag or wrinkle as it dries. You may also notice the varnish becoming tacky or sticky, which means that there is too much humidity or moisture in the air.
Rough Surfaces, Cold and Using Too Much Varnish
Varnish appears "silky" if you apply it to a rough or grainy surface. The varnish will adhere to itself, causing the silky rippling.
If your varnish looks "sandy" or "seedy," the varnish chilled in a cold environment. Make sure to store the varnish at temperatures between 70 and 80 degrees. You will also notice the sandy or seedy finish if you use the bottom liquid in a varnish can because particulate often settles at the bottom of a varnish can. Inspect the varnish in old cans before applying it to a wood surface.
A common error is using too much varnish. Varnish will chip, crack or flake if you apply too many coats of varnish on a wood surface. This may also occur if you apply dramatically different types of varnish on top of one another. You need to apply "elastic" varnish as a base coat, adding additional coats of progressively "less elastic" varnishes on top of each other as you build the finish.
Milky, Colored and Blistering Varnish
Milky or foggy varnish occurs when you allow too much moisture in the environment as you apply the varnish. This may occur from water spots dropping into the varnish or may even occur from placing an overheated item on top of the varnished surface. Make sure you have adequate ventilation when applying varnish.
Yellow, green or blue varnish problems are rare and occur when there is a coal gas in the air. This problem is more typical if you apply varnish to an automobile where the gas is more common.
Blistering varnish problems arise in overly warm environments, which cause the underlying wood to expand and release air into the drying varnish. Make sure to apply varnish on cooler days when the temperatures are near 70 degrees.